The boxes were used to carry valuables, scientific instruments, weapons and data. When the Copernicus passes Beta Lyrae the stasis box suddenly glows, indicating a second box is hidden somewhere in that system. Spock remarks, "Stasis boxes and their content are the only remnant of the species which ruled most of the galaxy a billion years ago. Their effect on science has been incalculable. In one was found a flying belt which was the key to the artificial gravity field used by starships. Another box contained a disruptor bomb with the pin pulled. As a result all stasis boxes are now under the jurisdiction of Starfleet and only certain key specialists handle them. The boxes are rare, potentially dangerous, and we seem to have found a second one."

The shuttle lands on an ice planet. Spock, Sulu, and Uhura exit the shuttle's aft airlock wearing life support belts. Unfortunately for them, hostile Kzinti lie nearby in ambush with an empty stasis box. The team are captured in a police web by a group of Kzinti and taken aboard their vessel. Spock tells the others that the lean, bedraggled one is a mind-reader. He tells Sulu that the Kzinti won't read his mind because Vulcans are herbivorous pacifists and Uhura a mere female. The Kzinti are meat eaters and if Sulu senses one trying to read his mind, he should think of eating raw vegetables. Spock advises Uhura to try to look harmless because Kzinti females are dumb animals. In an emergency they may forget a Human female is an intelligent creature, giving them a chance to escape. At first, Uhura is irritated by this, telling Spock "Thanks. Thanks a lot!" Spock then reminds Uhura that while he does indeed value her intelligence, they may have a better chance at escape if the Kzinti thinks she has none. Uhura understands Spock's instructions and quietly agrees.

Their captors are led by Chuft-Captain, who commands the Traitor's Claw. Their archaeologists had found an empty stasis box, but discovered it was a good way to draw others there. In the opened box they find a picture of a Slaver, some fresh meat, and a weapon created by the Slavers.

"First officer's log, supplemental. The Kzinti now possess a weapon potentially deadly to the entire galaxy. The extent of its power remains to be seen."

The Kzinti return to the surface to test the weapon. They run through settings similar or inferior to present technology. One setting disengages the police web, giving the team a chance to flee; in the process, Spock kicks Chuft-Captain in his ribs, recovers the weapon from him and runs away, but Uhura is stunned and recaptured by the Kzinti. Sulu and Spock regroup some distance from the ship, in the shadow of an outcropping of rock and ice. Spock explains that his striking Chuft-Captain was a calculated move, dishonoring the Kzin and preventing him from calling for help. Sulu tells Spock he believes the weapon belonged to a spy. Spock is initially skeptical that even someone with Sulu's knowledge of weaponry could make such a determination so quickly, but agrees upon hearing his explanation – only one of the various settings, a relatively weak laser, would be of any real use to a common soldier – and concludes that, therefore, it should also have a self-destruct setting. Before he can find it, Chuft-Captain hails them wanting to trade Uhura's life for the weapon. He also wants to engage in combat with Spock to regain his honor. Spock estimates his chances of defeating the Kzin are low, and Sulu refuses on Spock's behalf through his communicator. As Spock tries another setting, the weapon releases a giant energy beam creating an enormous explosion far away. Sulu exclaims, "We can't give them THAT!" Spock observes, "Fascinating. No world in the Federation has produced anything so powerful. Almost beyond theoretical limits. Total conversion of matter to energy at a distance." Sulu remarks, "If the Kzinti had that, the whole galaxy would be their dinner table!" The shock wave from the explosion knocks Spock and Sulu off their feet, and the Kzinti quickly recapture them and the weapon.

The Kzinti find another mode for the weapon, a "reasoning computer", a remarkable achievement for hand-held equipment. It gives few details of its origin and abilities, alluding to long-ago war. The weapon says that unless it is supplied with "certain code words" it will answer no further questions. Chuft-Captain demands the total-conversion beam, but Spock observes that the setting the computer gives him is not the same as the one he and Sulu observed earlier. As the Kzinti go outside to test the weapon, leaving the prisoners alone in the web, Spock explains his reasoning to Uhura. Awakened after an indeterminate time and surrounded by beings that do not know its proper protocols, it has decided to self-destruct to keep vital tactical information from falling into enemy hands. The Slaver weapon detonates, killing the Kzinti in a massive (but conventional) explosion. Standing on the rim of the crater left in the ice, Sulu laments the loss of a fine museum piece, but Spock observes that it would have been far too dangerous to place the weapon in a museum.

The Enterprise crew resume their journey in the Copernicus. Spock observes how an artifact of an ancient war almost ignited a new one for possession of it, and Uhura jokes that the Kzinti might never get over their superstition about "haunted" weapons.

"Mr. Spock, if it takes a stasis box to find another stasis box, how did anyone ever find the first one?
"As with a number of discoveries, purely by accident, lieutenant."

- Sulu and Spock

"Lieutenant Uhura, this may be crucial – in the presence of the Kzinti, do not say anything, do not do anything startling – try to look harmless."
"Any special reason?"
"Are you forgetting Kzinti females are dumb animals? In an emergency, the Kzinti may forget a Human female is an intelligent creature."
(Indignant)"Thanks – thanks a lot!"
"Lieutenant, I value your intelligence, but we may be able to seize an opportunity to escape if the Kzinti believe you have none."
(Understanding)"Yes, sir."

- Spock and Uhura

"Captain, he is too alien! He makes me taste yellow root munched between flat teeth!"
"Be glad if you need not read the Vulcan's mind."

- Kzin Telepath and Chuft-Captain

"What of the picture?"
"The Human, Sulu, believes it to be Slaver."
"So do I. It would have made a worthy enemy."

- Chuft-Captain and Kzin Telepath

"I have the weapon."
"They've got Uhura – and subspace radio. They can call for help from the Kzin planet if they think the weapon's worth it."
"No...they can not – or, rather, will not."
"Why?"
"Because I kicked Chuft-Captain. Consider. Chuft-Captain has been attacked by an herbivorous pacifist, an eater of leaves and roots, one who traditionally does not fight. And the ultimate insult, I left him alive. Chuft-Captain's honor is at stake. He must seek personal revenge before he can call for help."
"That gives us some time. You did plan it that way?"
"Of course."

- Spock and Sulu

"I have a feeling, Mr. Spock. This weapon must have belonged to a spy – an espionage agent."
"I acknowledge your expertise in the field of weapons, Mr. Sulu, but I do not see how you can determine probable ownership."
"Well, here – look at it. All these settings – we don't know a common Slaver soldier couldn't handle them, but as a weapon, only the laser is effective. The others aren't necessary for the line soldier's one purpose: to destroy the enemy."
"Assuming it's a spy weapon, then, the Slavers would have wanted to keep it a secret. If so, it is logical to assume that it has a self-destruct setting too."
"But we've seen all the phases."
"Perhaps not. There is the null setting. It seems to do nothing – but why should it be there?"

- Sulu and Spock

"We have the female prisoner as hostage. You have something we want. We will trade her life for the Slaver weapon."

- Chuft-Captain

"I compute the odds of my defeating Chuft-Captain in combat at sixteen to one against."
"Offer refused."
"They think very little of you."
"Wrong, they don't think much of YOU."

- Spock, Sulu, Chuft-Captain, and Uhura

"The Kzinti have legends of weapons haunted by their owners."
"Could it be a voice-activated mechanism?"
"No. It appears to be conversing with them. A reasoning computer that small!"

- Spock and Uhura

"How long has it been since you were turned off?"
"I do not know. When I am off I have no sense of passing time."
"What is the last thing you remember?"
"We were on a mission. I may not tell you of it unless you know certain code words."

- Chuft-Captain and The Slaver Weapon

"We can't let them have that weapon!"
"They are not about to get it, lieutenant."
"Why not?"
"Assume you are a Slaver war computer. You've been turned off – you do not know for how long – but when you were turned off, there was a war on. Now you are awakened by aliens you never saw before. They do not know any of the military passwords. They ask you so many questions, it is obvious they know little about you. Your owner is nowhere about. What would you think?"
"I'd think I'd been captured by the enemy, or an enemy at least."
"And when they asked you how to find your most powerful weapon setting, what would you give them?"
(Chuft-Captain pulls the trigger, and the question is answered in an explosive manner)

- Uhura, Spock, and Sulu

"No sign of the weapon, of course... it would've looked nice in some museum..."
"It never would've reached a museum, lieutenant. There was too much power in that one setting – if not the Kzinti, the Klingons or some other species would've tried to possess it."

David Gerrold remembered how noted science fiction author Larry Niven came to write this episode; "By then, [story editor] Dorothy ["D.C."] Fontana knew Larry Niven, and so when it was time to do the animated Star Trek, she was a BIG fan of Larry's, and said, 'Gee, I'd love to get a Larry Niven story, could we adapt one of your stories, Larry?' And that's when the deal was made." [1] Fontana herself said, "I thought bringing Larry Niven in was a good move, again to have that connection to the science fiction community. He was the one person who had an almost perfect story for us." (Star Trek: The Magazine Volume 1, Issue 16, p. 67) The story in question was "The Soft Weapon" – a science fiction, non-Star Trek short story that was notably republished in Niven's collection of stories Neutron Star in 1968 (having first been published in 1967) and is set in his Known Space universe.

Following D.C. Fontana's invite to write for the animated Star Trek, Larry Niven proposed two plot ideas that went undeveloped, as both had content that was deemed to be too problematic for the series. Shortly thereafter, Niven and Fontana were spending part of an afternoon at Gene Roddenberry's residence when Roddenberry suggested that Niven rewrite "The Soft Weapon" as an episode. (Playgrounds of the Mind) Fontana reflected, "We told Larry, 'Just write it, but put in our characters. You can put in the Kzin and all that.'" (Star Trek: The Magazine Volume 1, Issue 16, p. 67) In retrospect, Niven remarked of the adaptation idea, "That worked." However, he was initially not entirely sold on the prospect of including in the episode the Kzinti, who feature in the original short story as well as elsewhere in the Known Space universe. "I thought hard before giving the Kzinti to the Star Trek universe," Niven acknowledged. "I did it because I thought it would be fun to see what others would do with them." (Playgrounds of the Mind)

Some changes were evidently made between "The Soft Weapon" and this adaptation. The characters in the original short story are: Jason Papandreou (which was changed to Lt. Sulu for the episode); Jason's wife, Anne-Marie (changed to Lt. Uhura for the episode); and the Pierson's Puppeteer Nessus, a manic-depressive member of a race of pacifistic herbivores (changed to Spock for the episode). The device was originally made by a species (the Tnuctipun) rebelling against the Thrintun ("Slaver") Empire. Although Chuft-Captain and the Kzinti Telepath are the only crew members from the Traitor's Claw who receive a name or designation here, the original short story names the other members of the vessel's crew as Flyer, who later carries Telepath, and Slaverstudent, who opens the box.

Larry Niven did not have to include all the series' main characters in this episode. For instance, he noted, "I was given permission to leave Kirk out." (Playgrounds of the Mind)

D.C. Fontana admitted that the Kzinti of this episode were easily shown on screen due to the fact that the episode was produced with animation rather than in live-action. However, Fontana also said, "We didn't do their stripes, because it's hard to animate stripes." [2] She elaborated, "The only thing we couldn't do [regarding drawing the alien creatures of TAS] was make the Kzin striped. We had big orange cats, but we couldn't put the stripes in because animating the stripes would have been far too expensive, so they were tabby cats without the stripes." (Star Trek: The Magazine Volume 1, Issue 16, p. 65) D.C. Fontana viewed the Kzinti during the episode's production period. (Star Trek: The Magazine Volume 1, Issue 16, p. 67)

The Traitor's Claw (and the Kzinti space suits) was painted pink because the director of this episode, Hal Sutherland, has a kind of color blindness. D.C. Fontana later speculated that Sutherland had probably thought the pink color of the craft was a shade of gray. ("Drawn to the Final Frontier – The Making of Star Trek: The Animated Series", TAS DVD)

This is one of two TAS episodes that do not feature James Doohan voicing the character of Montgomery Scott (the other installment being "The Jihad", in which the character does appear but has no lines). Doohan provided voices for all of the Kzinti, however.

This is the second of three times in Star Trek: The Animated Series when the character of Arex does not appear. He also does not feature in "Yesteryear" and "The Jihad".

This is the only animated Star Trek episode that does not feature the Enterprise, apart from in credits sequences. It is the second of three animated episodes that do not feature any scenes set on the ship's bridge, the others being "Yesteryear" and "The Jihad".

The death of the Kzinti during this episode's conclusion marks the only time any characters are killed on screen during The Animated Series.

In his log at the end of the episode, Spock states that the weapon might have caused a war between "Man" and Kzinti. In Larry Niven's "Known Space Universe" (but not in "The Soft Weapon"), the Human-Kzinti conflicts are referred to as "The Man-Kzin Wars." (This is also the common title of numerous anthologies of short stories set in Niven's "Known Space Universe", mostly written by other authors; all such volumes except the very first are identified by Roman numerals indicating which volumes they are.)

Larry Niven once noted that he turned out to be correct in his estimation that it would be fun to see what others did with the Kzinti he had created. (Playgrounds of the Mind)

Having been too busy to see the Kzinti ship during production, D.C. Fontana only learned of the error in the colorizing of the Traitor's Claw when she watched this episode's broadcast. (Star Trek: The Magazine Volume 1, Issue 16, p. 67; "Drawn to the Final Frontier – The Making of Star Trek: The Animated Series", TAS DVD) The inappropriateness of the craft's color startled Fontana, at that point. ("Drawn to the Final Frontier – The Making of Star Trek: The Animated Series", TAS DVD) She immediately called Larry Niven and apologized to him, feeling a need to do so. ("Drawn to the Final Frontier – The Making of Star Trek: The Animated Series", TAS DVD; [3]) "The next day we were in," Fontana continued, referring to the series' regular production staff, "I said, 'What the heck happened with the ship? Why is it pink?'" It was shortly thereafter she learned that the production error had been due to Hal Sutherland's colorblindness. (Star Trek: The Magazine Volume 1, Issue 16, pp. 67-68) Years later, she referred to the mistake as "the only problem" with the episode. [4] She also enthused, "I thought it turned out to be a very good episode – interesting and different [...] [with] these wonderful aliens." (Star Trek: The Magazine Volume 1, Issue 16, p. 67)

David Gerrold similarly once opined that this episode's crossover between the Star Trek and the Known Space universes "was very, very good." [5]

Also, this episode stuck in author Allyn Gibson's memory as being the first Star Trek production he saw. He described the installment as a "classic episode." [6]

The editors of Trek magazine collectively scored this episode 4 out of 5 stars (a rating that they termed "very good"). (The Best of Trek #1, p. 111)

In The Star Trek Files magazine, John Peel remarked, "A fascinating tale, for several reasons. Firstly, it employs only three of the main cast, and Kirk isn't even mentioned this time around. The three we do see are all treated well, and come across as intelligent and capable, which is enjoyable. Secondly, the tale itself is fascinating [....] It adapts well, and fits nicely into this Star Trek universe. The idea of a multi-changeable weapon (actually meant for use by a spy) is clever, and the idea works out well. In fact, the story centers almost totally about this, since the three main characters are locked up most of the time!" (The Star Trek Files: The Animated Voyages End, pp. 23 & 24-25)

In Star Trek: The Official Fan Club Magazine issue 87, p. 6, critic Philip Chien commented that "the story translated quite nicely" between its original incarnation as "The Soft Weapon" into this televised adaptation, while also believing that the Kzinti depicted in this version "seemed much less threatening than their written descriptions."

The unauthorized reference bookBeyond the Final Frontier (p. 57) cites this as one of three installments from the animated series that "stand out from the pack" (the others being "More Tribbles, More Troubles" and "Yesteryear"). The book also describes this outing as "a fairly uncompromising burst of real science fiction" and proposes that, in common with "More Tribbles, More Troubles", it would have made a "great live-action" episode.